Adaptive enhanced cell identity positioning (AECID), as described, e.g., in the patent application PCT/SE2005/001485, is a positioning technology that refines the basic cell identity positioning method in a variety of ways. The AECID positioning method is based on the idea that high precision positioning measurements, e.g. assisted GPS (A-GPS) measurements, can be seen as points that belong to regions where certain cellular radio propagation condition persist. In its simplest form A-GPS measurements that are performed at the same time as a certain cell ID is valid represent A-GPS measurements that fall within a specific cell of a cellular system. The AECID positioning method recognizes this and introduces a tagging of high precision measurements according to certain criteria. This may for instance include                the cell IDs that are detected by the terminal that performs the high precision position measurement,        the quantized path loss or signal strength measurements, wrt. to multiple radio base stations (RBSs), performed by the terminal that performs the high precision position measurement,        the quantized Round Trip Time (RTT, in WCDMA) or Timing Advance (TA, in GSM),        the quantized noise rise, representing the load of a code division multiple access (CDMA) system,        radio connection information, e.g. the radio access bearer (RAB),        quantized time.        
It is important to note that tags consist of vectors of indices, each index taking an enumerable number of discrete values. Continuous variables used for tagging, like path loss, hence need to be quantized.
The second step of the AECID positioning method is to collect all high precision positioning measurements that have the same tag in separate high precision measurement clusters. It is clear that each such cluster consists of high precision position measurements collected from a region with similar radio conditions—hence the measurements are normally from the same well defined geographical region. More specifically, said geographical region is normally substantially smaller than the extension of a cell of the cellular system.
In a third step of the AECID positioning method, a polygon that represents the geographical extension of a cluster is computed, for each stored high precision position measurement cluster. The two most pronounced properties of the algorithm include that the area of the polygon is minimized (accuracy hence maximized) and that the probability that the terminal is within the polygon (the confidence) is precisely known (it is set as a constraint in the algorithm).
So far, steps towards the creation of a tagged database of polygons have been described. An AECID position is now easily determined by a first determination of the persisting tag. This is performed by looking up cell IDs, by performing auxiliary measurements and by looking up auxiliary connection information, as described above. The polygon corresponding to the determined tag is then looked up in the tagged database of polygons and followed by a reporting, e.g. over the RANAP interface as described in the document 3GPP TS 25.413, “UTRAN Iu interface Radio Access Network Application Part (RANAP) signaling”, using the polygon format.
The preferred representation of the geographical extension of the cell is given by the cell polygon format. The extension of a cell is described by 3-15 corners of a closed polygon which does not intersect itself, cf. FIG. 2. The format is two-dimensional and the corners are determined as pairs of longitudes and latitudes in the WGS84 geographical reference system. The exact messaging format is described by FIG. 3. It should be noted that due to the complexity of the radio propagation the cell polygon format is only an approximation of the extension of the true cell. The selection of the polygon format is dictated by the need to have a reasonably flexible geographical representation format taking, e.g., computation complexities and reporting bandwidths into account. Since the polygon format approximates the cell extension, the polygon is normally pre-determined in the cell-planning tool to represent the cell extension. The underlying off-line calculation of the cell polygon can, e.g., be based on coverage simulations of varying levels of sophistication. However, the end result is normally not very reliable when the confidence of the calculated cell extension is considered.
High precision positioning methods are used to denote positioning methods that have a potential to meet the North-American E-911 emergency positioning requirements. Methods that meet these requirements are capable of obtaining positioning accuracies of either (terminal based) 50 meters (67%) and 150 m (95%), or (network based) 100 meters (67%) and 300 m (95%).
Assisted GPS (A-GPS) positioning is an enhancement of the global positioning system (GPS). An example of an A-GPS positioning system is displayed in FIG. 4. There GPS reference receivers attached to, e.g., a cellular communication system collect assistance data that, when transmitted to GPS receivers in terminals connected to the cellular communication system, enhance the performance of the GPS terminal receivers. Typically, A-GPS accuracy can become as good as 10 meters also without differential operation. However, the accuracy becomes worse in dense urban areas and indoors, where the sensitivity is most often not high enough for detection of the very weak signals from the GPS satellites.
Similarly to A-GPS the uplink time difference of arrival (UTDOA) positioning method is based on time of arrival measurements. However, in the UTDOA case measurements of transmissions from the UEs are performed in several RBSs. An advantage with UTDOA as compared to A-GPS is the fact that the signal strengths are higher, something that enhances the ability to perform positioning indoors. The accuracy of UTDOA is expected to be worse than that of A-GPS though, mainly because the radio propagation conditions are worse along the surface of the earth than when GPS radio signals are received from satellites at high elevation angles. For various reasons U-TDOA is also an expensive technology to deploy. There is also a counterpart to UTDOA specified by 3GPP and operating in the downlink, i.e. measurements of time of arrivals of radio signals transmitted by several RBSs are performed in the UE. In practice, however, this OTDOA-IPDL method lacks the sensitivity to provide any useful high precision performance.
Currently, it appears that A-GPS is becoming the dominating technology to obtain high precision positioning services. For the AECID method, the consequence is a difficulty to obtain high precision position reference measurements from indoor environments, a fact that will reduce applicability and accuracy of AECID positioning significantly. One alternative is to use dedicated personnel for surveying purposes, i.e. to make manual high precision positioning measurements in support of AECID. This is in fact the only known alternative for a cellular operator that has not deployed any other high precision positioning method than A-CPS. A disadvantage with manual measurements is that it requires dedicated personnel and equipment, both of which are expensive. The latter is particularly true since large areas needs to be surveyed to achieve a complete AECID coverage.